The emergence of silymarin (SMN) as a natural remedy for liver diseases, coupled with
its entry into NIH clinical trial, signifies its hepatoprotective potential. SMN is
noted for its ability to interfere with apoptotic signaling while acting as an antioxidant.
This in vivo study was designed to explore the hepatotoxic potential of Doxorubicin
(Dox), the well-known cardiotoxin, and in particular whether pre-exposures to SMN
can prevent hepatotoxicity by reducing Dox-induced free radical mediated oxidative
stress, by modulating expression of apoptotic signaling proteins like Bcl-xL, and
by minimizing liver cell death occurring by apoptosis or necrosis. Groups of male
ICR mice included Control, Dox alone, SMN alone, and Dox with SMN pre/co-treatment.
Control and Dox groups received saline i.p. for 14 days. SMN was administered p.o.
for 14 days at 16 mg/kg/day. An approximate LD(50) dose of Dox, 60 mg/kg, was administered
i.p. on day 12 to animals receiving saline or SMN. Animals were euthanized 48 h later.
Dox alone induced frank liver injury (>50-fold increase in serum ALT) and oxidative
stress (>20-fold increase in malondialdehyde [MDA]), as well as direct damage to DNA
(>15-fold increase in DNA fragmentation). Coincident genomic damage and oxidative
stress influenced genomic stability, reflected in increased PARP activity and p53
expression. Decreases in Bcl-xL protein coupled with enhanced accumulation of cytochrome
c in the cytosol accompanied elevated indexes of apoptotic and necrotic cell death.
Significantly, SMN exposure reduced Dox hepatotoxicity and associated apoptotic and
necrotic cell death. The effects of SMN on Dox were broad, including the ability to
modulate changes in both Bcl-xL and p53 expression. In animals treated with SMN, tissue
Bcl-xL expression exceeded control values after Dox treatment. Taken together, these
results demonstrated that SMN (i) reduced, delayed onset, or prevented toxic effects
of Dox which are typically associated with hydroxyl radical production, (ii) performed
as an antioxidant limiting oxidative stress, (iii) protected the integrity of the
genome, and (iv) antagonized apoptotic and necrotic cell death while increasing antiapoptotic
Bcl-xL protein levels and minimizing the leakage of proapoptotic cytochrome c from
liver mitochondria. These observations demonstrate the protective actions of SMN in
liver, and raise the possibility that such protection may extend to other organs during
Dox treatment including the heart.
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